It is known that reduced coenzyme Q10 can be prepared by producing coenzyme Q10 in the conventional manner, for example by synthesis, fermentation, or extraction from natural products, and concentrating a reduced coenzyme Q10-containing eluate fraction resulting from chromatography (JP-Hei-10-109933-A) On that occasion, as described in the above-cited publication, the chromatographic concentration may be carried out after reduction of oxidized coenzyme Q10 contained in the reduced coenzyme Q10 with a conventional reducing agent such as sodium borohydride or sodium dithionite (sodium hyposulfite), or reduced coenzyme Q10 may be prepared by reacting the reducing agent mentioned above with an existing highly pure grade of coenzyme Q10.
However, the thus-obtained reduced coenzyme Q10 cannot always be in a highly pure state but tends to occur as a low-purity crystalline, semisolid, or oily product containing such impurities as oxidized coenzyme Q10. Thus, even if a reaction product of reduced coenzyme Q10 containing no or few oxidized coenzymes Q10 is obtained in a reduction reaction, it is very difficult to obtain a high-quality reduced coenzyme Q10 crystalline.
And, reduced coenzyme Q10 is readily oxidized to oxidized coenzyme Q10 by molecular oxygen. On a commercial production scale, complete oxygen elimination is very difficult to achieve and, furthermore, fairly long periods of time are required for individual operations, unlike laboratory scale production, so that residual oxygen exerts a great adverse effect. The oxidation in question is directly connected with such yield and quality problems as the formation of hardly eliminable oxidized coenzyme Q10 and adulteration of the product therewith.
Thus, it is a very important task to stabilize reduced coenzyme Q10, namely to protect the same against oxidation. Up to the present, however, no commercial grade of reduced coenzyme Q10 has been on the market, so that how to preserve reduced coenzyme Q10 stably, for instance, has been scarcely made. Only there is found WO 01/52822 A1 describing the use of a reducing agent in a method of stabilization and in a composition.